BNETWORK TROUBLESHOOTING METHODOLOGYEXAM OBJECTIVES IN THIS CHAPTERHOW TO USE THE OSI MODEL IN TROUBLESHOOTING 575TROUBLESHOOTING THE PHYSICAL LAYER 581TROUBLESHOOTING THE DATA LINK LAYER 591TROUBLESHOOTING THE NETWORK LAYER 598TROUBLESHOOTING THE TR...
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Network Troubleshooting Methodology
ExAM oBJECTIvES IN ThIS ChApTEr
how To uSE ThE oSI ModEl IN TrouBlEShooTING 575TrouBlEShooTING ThE phySICAl lAyEr 581TrouBlEShooTING ThE dATA lINK lAyEr 591TrouBlEShooTING ThE NETworK lAyEr 598TrouBlEShooTING ThE TrANSporT lAyEr 603TrouBlEShooTING ThE SESSIoN lAyEr 609TrouBlEShooTING ThE prESENTATIoN lAyEr 612TrouBlEShooTING ThE ApplICATIoN lAyEr 614INTroduCTIoN
Congratulations! You’ve made it almost all the way through the Network+ exam preparation guide. You’ve learned all about the physical and logical components that make up a network, and how to install and configure the Transmission Control Protocol/Internet Protocol (TCP/IP) suite. You’ve also learned about the different protocols that make up the TCP/IP suite as well as how they map to the Open Systems Interconnect (OSI) model. This includes the Internet Protocol (IP), which is the workhorse of the TCP/IP suite that handles the “heavy lifting” of routing TCP/IP traffic from one host to another. You’ve also learned about TCP/IP’s two session layer protocols: TCP, and the User Datagram Protocol (UDP). TCP is a connection-oriented protocol that’s used when each session layer packet has to be acknowledged by the computer it’s being sent to. UDP is connectionless, which is useful for low-overhead connections where speed is at a premium. You’ve also seen the Internet Control Message Protocol (ICMP), which is used for TCP/IP trouble-shooting. In our last chapter, we talked extensively about the various utilities that are available to troubleshoot connectivity problems on a network. In our 573them in a real-world situation to troubleshoot network connectivity issues. We will revisit the OSI model and the TCP/IP-based Department of Defense (DoD) model. We’ll also review the components of the suite of protocols that make up the TCP/IP stack and how common connectivity devices, such as repeaters, bridges, routers, and switches are used to expand or segment TCP/IP networks. All of this is critical information to have at your fingertips when you’re troubleshooting because, just as a physician is better able to treat a sick patient if he knows the person’s background, characteristics, and how the patient normally behaves when he is not ill, you will be at a big advantage when you’re confronted with “sick” or a badly functioning network if you understand your network’s “anatomy” and components. Most networks depend on the TCP/IP protocol to communicate, making it one of the most important “body parts”.The objective of this chapter is to give you a detailed review of TCP/IP, and explain the methodology that will enable you to recognize symptoms of network troubles and to diagnose and correct any errors or misconfigurations that you may find. We all know that a healthy network makes for a happy network administrator, and the information you find in this chapter will help you in preparing both for the Network+ exam and for your journey into the real world of network administration and troubleshooting. To help you with this, we will first go through each layer of the OSI model and talk about the different troubleshooting steps you can take at each layer. For example, the physical layer is concerned with physical connectivity between two computers, so here you’ll look for broken cables or a malfunctioning network interface card (NIC). The data link layer is where switches, bridges, and Ethernet frame types operate, so you’ll troubleshoot this layer by examining all of these components. We will start our review at the physical layer, which is the lowest layer of the OSI model, and work all the way up through the application layer. This chapter will help you to put together all of the concepts you’ve learned throughout this study guide, to help you use them in troubleshooting real-world issues that you might encounter on a network.Exam warningBe sure that you really understand what is happening at each layer of the OSI model.
It’s important for the Network+ exam that you’re able to recognize the different network
protocols and devices that operate at each level, rather than just memorizing the “Please
Do Not Throw Sausage Pizza Away” or “All People Seem To Need Data Processing”
mnemonics.